This application is based on and incorporates herein by reference Japanese Patent Application No. 2002-337085 filed on Nov. 20, 2002.
1. Field of the Invention
The present invention relates to an accumulation type fuel injection system for injecting high-pressure fuel accumulated in a common rail through injectors.
2. Description of Related Art
An accumulation type fuel injection system calculates an injection quantity of fuel injected from an injector in accordance with an operating state of an engine. For instance, as for a fuel injection quantity during a normal operation, a basic injection quantity is calculated in accordance with an accelerator position and engine rotation speed. Then, a target injection quantity Qfin is calculated by correcting the basic injection quantity in accordance with effects of engine water temperature, a supercharging pressure, the atmospheric pressure, fuel temperature and the like.
As for a pressure in a common rail (a common rail pressure, hereafter), a basic pressure P is calculated in accordance with the target injection quantity Qfin and the engine rotation speed. Then, a target pressure Pfin is calculated by correcting the basic pressure P in accordance with the engine water temperature, the supercharging pressure, the atmospheric pressure, the fuel temperature and the like.
When acceleration is stopped and in consequence the actual common rail pressure NPC becomes higher than the target pressure Pfin, or a pressure difference xcex94P therebetween becomes great, noise is generated by high-temperature combustion. Such noise is generated when a large amount of heat is generated during short-period combustion.
A control device regulates a discharging quantity of the high-pressure fuel discharged by a supply pump, which supplies the high-pressure fuel to the common rail. Thus, the supply pump maintains the common rail pressure at the target pressure Pfin. The supply pump has a function of increasing the common rail pressure to the target pressure Pfin. When pressure reduction of the common rail is required, the supply pump can stop the fuel discharge. However, the supply pump has no function to reduce the common rail pressure actively.
For instance, in deceleration immediately after high-speed travel, fuel injection under a low pressure is required abruptly in a state in which the fuel injection has been performed at high speed and under a high pressure. However, until the common rail pressure is decreased to the low pressure through the fuel injection or fuel leak from the injector, the fuel injection is performed under a condition that the actual common rail NPC is higher than the normally required target pressure Pfin, or under a condition that the pressure difference xcex94P therebetween is large.
Under the condition that the actual pressure NPC is higher than the target pressure Pfin, an injection period is extremely contracted. Thus, the noise is generated in the combustion, in which a large amount of heat is generated in a short period. The generation of the high-temperature combustion is not preferable for performance of the vehicle, too.
As a technology for avoiding the above problem, a technology for mounting a pressure reduction valve to the common rail or a high-pressure fuel pipe for reducing and regulating the common rail pressure is known. Thus, the actual pressure NPC is quickly reduced to the target pressure Pfin by returning the high-pressure fuel accumulated in the common rail to a fuel tank when the target pressure Pfin is decreased rapidly.
As means for reducing the common rail pressure without employing the pressure reduction valve, a technology for driving an electromagnetic valve of the injector to open for a period shorter than a period required to open the injector so that the injector performs an invalid injection is known, for instance, as disclosed in Japanese Patent Application Unexamined Publication No. H11-173189. Thus, the high-pressure fuel flowing into a control chamber of the injector from the common rail is leaked to the fuel tank, so the common rail pressure is reduced.
In the technology using the pressure reduction valve, the pressure reduction valve has to be attached to the common rail or the high-pressure fuel pipe. As a result, mounting performance of the common rail to the vehicle is degraded because of the addition of the pressure reduction valve. Meanwhile, the cost is increased because of the increase in the number of parts or an increase in assembling processes.
In the technology for performing the invalid injection through the injector, the common rail pressure is reduced gradually. Therefore, the actual pressure NPC cannot be reduced to the target pressure Pfin quickly. As a result, the noise is generated by the high-temperature combustion in an early stage of the pressure reduction.
It is therefore an object of the present invention to provide an accumulation type fuel injection system capable of alleviating noise caused by high-temperature combustion, which is caused when an actual common rail pressure is higher than a target pressure suitable for an operating state, without causing an increase in a number of parts or degradation of mounting performance due to addition of a pressure reduction valve.
According to an aspect of the present invention, an accumulation type fuel injection system slackens combustion by controlling fuel injection performed by an injector when high-temperature combustion is predicted by high-temperature combustion predicting means. Thus, noise generated by the high-temperature combustion can be alleviated.
More specifically, the noise, which is caused by the high-temperature combustion when an actual common rail pressure is higher than a target pressure suitable for an operating state, can be alleviated without causing an increase in a number of parts or degradation of mounting performance due to addition of the pressure reduction valve.